The invention relates to a composition preparation method for preparing a composition of estolides, the method comprising reacting an unsaturated compound of a type such as an acid or ester, with a saturated fatty acid; in the presence of a catalyst of a type such as sulphonic acid, the said method including no vacuum distillation step thereby making it possible to separate the monoestolides from the polyestolides. The invention also relates to a composition of estolides that is obtainable by the method according to the invention and the use thereof in lubricating compositions.